“We are not offering a quick fix,” he cautioned in the preface of a 53-page report. “Rikers Island cannot be closed overnight.”

But there's a vast difference between overnight and the mayor's 10-year timetable, and his report only amplified criticism from criminal-justice reformers that he is not acting with urgency.

The jail's average daily population of 9,400 is its lowest in more than two decades. But the number must drop to 5,000 before the city can close it, according to the mayor's plan, which sets an interim target of 7,000 within five years.

“It would be much simpler for us to tell people what they want to hear and say we can achieve this goal quickly and easily, but we won’t do that," the mayor says in the report. “Instead, we are realistic.”

Advocacy groups contend the mayor is overstating the challenge.

“Plans and policies for reducing the city’s jail population and closing Rikers already exist,” said Alyssa Aguilera, co-executive director of VOCAL-NY, in a statement. “What we need now is the political will and a swift timeline to enact change.”

City Councilman Rory Lancman called the mayor's report "a political document" that does not establish a path to closing Rikers within a decade.

"Let there be no doubt: New York City can close Rikers Island in less than 10 years, if we have the leadership and political will required to do so," he said in a statement.

The de Blasio administration listed special bail programs, more jail alternatives and community service for detainees sentenced to fewer than 30 days as strategies to reduce incarceration.

About 44% of the population consists of detainees held for over 270 days, according to the city. And around 85% of Rikers’ detainees are awaiting trial.

Criminal justice reformer Robert Gangi, who is challenging de Blasio in the Democratic primary, said the mayor's Rikers plan falls well short of what is needed. He suggested the decriminalizing offenses such as fare evasion, marijuana possession and sex work.

“Instead of demonstrating the bold leadership needed, de Blasio, claiming to be realistic, punts,” Gangi said in a statement.

The city will add $2.3 million in funding for its supervised release program, which lets low-risk defendants stay home while they await trial. It was rolled out in March 2016 as a $17.8 million initiative.

The mayor’s Rikers plan also allots $2.5 million to transitional housing for homeless women admitted to jails. About 630 women (homeless or not) are in custody on an average day, according to the report.

In the plan, de Blasio also introduces a Justice Implementation Task Force, led by Director of the Mayor’s Office of Criminal Justice Elizabeth Glazer and Corporation Counsel Zachary Carter, to brainstorm other ways to reach the 5,000 daily population goal.

Studies have shown shutting down the complex would save the city money as well. It costs $300 million annually just to transport people to and from the island.

A commission recently estimated that reducing the inmate population would save $540 million in annual operating costs after 10 years.

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